Various processes are known for forming weld connections between plastic components, i.e., polymeric components which are thermoplastic in nature. In one such technique, a welding muff with concealed or embedded wires forming a heating coil is fitted over the abutting ends of two plastic pipes to be joined so that the ends at the connection point can be melted and recooled, forming a tight connection.
Because pipes and welding muffs of different diameters and correspondingly different welding energy requirements are to be handled, the current supply devices must be adjustable so as to be adaptable to these different operation parameters. Heretofore, apparatus of this sort is adjusted in accordance with the nominal width or diameter of the welding muff and then supplied with a heating current at constant operating voltage for a predetermined time interval, the total heating energy supplied thus being the product of current, voltage and time.
With such known devices, however, there is a significant danger that the operator can make an error and can set into the apparatus an incorrect nominal width or diameter so that either too much or too little heat energy is supplied, either of which can lead to an improper weld.
A monitoring device for plastic welding devices is shown in Swiss patent document No. 523,130 wherein a desired value corresponding to the heat energy required for the relevant sizes of the connections or of the coil is set by a setting means. It is monitored only as to whether the given weld energy corresponding to the set "theoretical" value was or was not correctly measured. Thus, erroneous operation still cannot be precluded.
With the process disclosed in Swiss patent document No. 518,790 or French patent document No. 2,077,990, only the welding time or the welding capacity dependent upon the surrounding temperature is modified such that the final temperature of the weld point independent of the surrounding temperature is substantially always the same. A theoretical or desired value, however, must also be set into the device so the quality of the weld, even in this apparatus, depends on the correct setting.